Following injury or primary cell culture, quiescent differentiated vascular smooth muscle (VSMDIFF) cells undergo phenotypic switching to a synthetic phenotype (VSMSYN) characterized by high rates of cellular proliferation, extracellular matrix remodeling, motility and pro-inflammatory function. This process includes changes in expression of channels and pumps involved in intracellular Ca2+ homeostasis, several of which have been targeted in vitro to inhibit vascular remodeling associated with injury and disease. A significant challenge is to understand how Ca signals are transduced to regulate VSMSYN -specific function. 2+ In previous funding periods we characterized expression and function of multifunctional serine/threonine Ca2+/Calmodulin-dependent protein kinase II (CaMKII) in VSM. We first discovered that expression of a CaMKII? splice variant was increased in rat VSM following arterial injury, functionally promoting VSM cell proliferation, migration and neointima formation. Conversely, CaMKII? expression rapidly decreases in parallel with VSMDIFF phenotype markers, conditional knockout results in enhanced vascular remodeling following vascular injury, and conversely over-expression inhibits VSMSYN function and vascular remodeling. (Preliminary studies). These results indicate that CaMKII? and ?-isoforms have non-equivalent functions in VSM. Novel preliminary studies suggest coordinate regulation of CaMKII?- by microRNA-30 family members and CaMKII? by promoter DNA methylation/de-methylation. It is hypothesized that reciprocal regulation of CaMKII?- and ?-isoform expression in VSM, and the relative isoform composition of CaMKII holoenzymes, is a determinant of vascular remodeling in response to injury and disease. Three related but independent specific aims are proposed to: Aim 1. establish cellular and molecular mechanisms underlying opposing CaMKII-isoform function in regulating arterial remodeling in response to injury using novel genetic mouse models, a femoral artery wire injury protocol, and in vitro cell culture studies; Aim 2. Using the same approaches, test a novel mechanism and functional consequences of reciprocal regulation of CaMKII? and ?-isoform expression by miR-30 and DNA cytosine methylation in vivo and in vitro; and Aim 3. Evaluate the functional importance of VSM cell CaMKII signaling and isoform dynamics in a clinically relevant context, i.e. the process of arteriovenous-fistula maturation and failure studied in a mouse model of AVF failure and correlated with analyses of human failed AVF specimens following surgical revision.